Java Hashset vs Hashmap

Java provides a wide range of data structures to store, organize, and manipulate data efficiently. Among these, HashSet and HashMap are two popular classes that are widely used for storing collections of objects. Both HashSet and HashMap belong to the Java Collection Framework and provide unique features that make them suitable for different applications.

HashSet is a class that provides a way to store a collection of objects where each object is unique. In HashSet, duplicate objects are not allowed, and the order in which the elements are stored is not guaranteed.

On the other hand, HashMap is a class that provides a way to store a collection of key-value pairs. Each key is unique, and its corresponding value can be accessed using the key. HashMap allows null values and a single null key.

This article aims to provide a detailed explanation of the differences between HashSet and HashMap classes in Java. The article will explain the definition, implementation, storing mechanism, and method of insertion of HashSet and HashMap classes.

The article will also highlight the performance differences between the two classes and their preferred uses. Additionally, the article will provide examples of HashSet and HashMap to help readers understand their features and usage better.

HashSet vs. HashMap

In Java, both HashSet and HashMap are important collection classes used for data structures. However, they differ in their definition, characteristics, and usage. Let’s take a look at each class in detail. HashSet is a collection that implements the Set interface. It generates a collection that stores data in a hash table. In HashSet, we store objects, and it does not allow duplicate values. It can contain a single null value.

HashMap is a hash table-based implementation of the Map interface. It is used to store key-value pairs. In HashMap, we store a key-value pair, and it maintains the mapping of key and value. It does not permit identical keys but does permit repeat values. It can have a single null variable and several null values.

Differences between HashSet and HashMap based on various parameters

HashSet and HashMap are two popular data structures used in Java, but they differ based on various parameters that can impact their usage. Here are some key differences between them:

• Implementation: HashMap implements Map, Cloneable, and Serializable interfaces. HashSet implements Set, Cloneable, Serializable, Iterable, and Collection interfaces.
• Storage Mechanism: HashMap stores objects using a hash table, while HashSet uses a HashMap object to store objects.
• Handling Duplicates: HashMap doesn’t allow duplicate keys but allows duplicate values. HashSet doesn’t allow duplicate values.
• Null Values: HashMap can contain a single null key and multiple null values, whereas HashSet can contain only a single null value.
• Method of Insertion: The put() method is used to add elements in HashMap, while the add() method is used for HashSet.
• Performance: HashMap is generally faster than HashSet since values are associated with a unique key. HashSet is slower than HashMap because the member object is used to calculate the hash code value, which can be the same for two objects.

By understanding these key differences between HashSet and HashMap, developers can choose the appropriate data structure for their specific needs.

Implementation of HashSet and HashMap

HashSet and HashMap are two popular collection classes in Java that have unique implementation strategies. In this section, we will explore how HashSet and HashMap internally implement their functionalities and the interfaces they implement.

HashSet and HashMap both implement Serializable, Cloneable, and Iterable interfaces. However, HashMap also implements the Map interface, which allows it to store key-value pairs. On the other hand, HashSet implements the Set interface, which means that it stores unique elements only.Both HashSet and HashMap use hashing to implement their functionalities. HashSet uses a hash table for storage, while HashMap uses a hash table to store its key-value pairs.In a hash table-based implementation, the collection is stored in an array-like structure.

The hash function maps each element of the collection to a unique index in the array. If two elements have the same hash code, they are stored in the same bucket, and a linked list is used to store them.

The hash function used by HashSet and HashMap is responsible for generating a unique hash code for each object in the collection. The hash code is used to locate the object’s index in the array. If two objects have the same hash code, they are considered equal by the collection.

Example code that demonstrates the implementation of HashSet and HashMap in Java:

import java.util.HashSet;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

public class HashSetHashMapExample {

    public static void main(String[] args) {

        // Implementation of HashSet
        HashSet<String> set = new HashSet<String>();

        // Adding elements to the HashSet
        set.add("Java");
        set.add("Python");
        set.add("C++");
        set.add("JavaScript");
        set.add("Ruby");

        // Displaying the elements of the HashSet
        System.out.println("Elements of the HashSet: ");
        Iterator<String> itr = set.iterator();
        while (itr.hasNext()) {
            System.out.println(itr.next());
        }

        // Implementation of HashMap
        HashMap<Integer, String> map = new HashMap<Integer, String>();

        // Adding key-value pairs to the HashMap
        map.put(1, "John");
        map.put(2, "Kate");
        map.put(3, "Mike");
        map.put(4, "Lily");
        map.put(5, "Tom");

        // Displaying the key-value pairs of the HashMap
        System.out.println("Key-value pairs of the HashMap: ");
        for (Map.Entry<Integer, String> entry : map.entrySet()) {
            System.out.println("Key: " + entry.getKey() + " Value: " + entry.getValue());
        }
    }
}

Output:
Elements of the HashSet:
Java
C++
JavaScript
Ruby
Python
Key-value pairs of the HashMap:
Key: 1 Value: John
Key: 2 Value: Kate
Key: 3 Value: Mike
Key: 4 Value: Lily
Key: 5 Value: Tom

In the above code, we have first implemented HashSet and then HashMap. We have created a HashSet of strings and added some elements to it. Then, we displayed the elements of the HashSet using an iterator.

Next, we have implemented a HashMap of integer keys and string values. We added some key-value pairs to it and then displayed the key-value pairs of the HashMap using a for-each loop and Map. Entry interface.
Both HashSet and HashMap use hashing internally to store elements efficiently. In HashSet, each element is hashed using its own hash code and stored in a bucket corresponding to the hash code. In HashMap, each key-value pair is hashed using the key’s hash code and stored in a bucket corresponding to the hash code.

Conclusion

In conclusion, HashSet and HashMap are two important classes in Java’s collections framework. HashSet is used to store a collection of unique elements, while HashMap is used to store key-value pairs. We have discussed the differences between HashSet and HashMap.

The differences between HashSet and HashMap are based on various parameters. They are implementation, storage mechanism, duplicate values, null values, method of insertion, and performance. We have also looked at the internal implementation of HashSet and HashMap, including the interfaces they implement and the hash table-based implementation.

In summary, HashSet and HashMap have their own unique use cases. It’s important to understand their differences to choose the appropriate one for your project. By understanding how they work behind the scenes, you can optimize your code for better performance. To learn more about Java collections, we recommend exploring the Java documentation. You may also consider reading books such as “Effective Java” by Joshua Bloch. Another recommended book is “Java Generics and Collections” by Naftalin and Wadler. Overall, mastering the use of HashSet and HashMap is essential for any Java programmer looking to write efficient and effective code.